The present invention relates generally to the field of coal gasification and, in particular, to a radiant synthesis gas (syngas) cooler for use in a coal gasification process. In one instance, the present invention relates to a radiant synthesis gas (syngas) cooler for an Integrated Gasification Combined Cycle (IGCC) power plant. In this embodiment, the radiant syngas cooler is used to contain and cool the synthesis gas produced by a coal gasification process used in the IGCC power plant.
IGCC power plants firing solid fuels have traditionally been higher capital cost and have had lower operating availability and reliability than competing solid fuel technologies such as pulverized coal combustion Rankine cycles. Primary components to be improved upon to make IGCC more competitive include uncooled gasifiers and radiant and convective synthesis gas coolers.
The radiant syngas cooler (RSC) is a component of an integrated gasification combined cycle (IGCC) power plant using the GE/Texaco entrained-flow coal gasification process. A stream of hot syngas and slag from the gasifier enters the RSC at 2300° F. to 2700° F. and operating pressure of 500 to 900 psia. The RSC recovers heat from the syngas to generate steam, and removes most of the entrained solids. The syngas leaves the RSC at 400° F. to 500° F., after which it goes to a gas cleanup system and the gas turbine for power generation.
In the first stage of the RSC, heat is recovered in a radiant boiler to generate high pressure saturated steam. The radiant boiler is a cylindrical enclosure constructed with water-cooled tubes and membrane, known as the “cage-wall”. There are several division walls, or platens, inside the cage-wall (also water cooled) to enhance radiant heat transfer from the gas. Syngas leaves the radiant boiler at 1100° F. to 1300° F. where it enters the second stage of the RSC, a water quench system that is used to separate the slag and particulate from the syngas and further cool the gas to the desired outlet temperature of 400° F. to 500° F. Finally, a large pressure vessel encloses the radiant boiler, steam generation system, water quench and slag removal systems, to maintain the system operating pressure. The cost of the RSC is overwhelmingly driven by the size of the pressure vessel. Therefore, reducing the size and weight of the vessel is critical to cost reduction.
An existing arrangement of platens (the straight, radially oriented, lines in FIG. 1) used in the Tampa Electric Polk Power Station Unit #1 is shown in the cross-section view of a radiant syngas cooler 10 of FIG. 8. In RSC 10 of FIG. 8, there are 12 division walls 30 that act as radial platens. These division walls, or radial platens, 30 are arranged like the spokes of a wheel, where such radial platens are uniformly spaced at intervals of 30 degrees. The design of RSC 10 will be explained in further detail below.
A similar, but slightly more compact RSC arrangement is shown in the RSC of FIG. 11, where the RSC is shown in simplified form with only the enclosure wall 28 and the radial platens 30 being shown (i.e., the platens 30 are shown as straight lines rather than illustrating the individual tubes that make-up such division walls, or radial platens, 30). In the case of the RSC of FIG. 12, there are 18 divisional walls, or radial platens, 30 that are uniformly spaced at intervals of 20 degrees. As would be appreciated by those of skill in the art, the RSC of FIGS. 11 and 12 illustrate known placement and number of division walls, or radial platens, 30. Regarding the design of FIG. 11, this design is the design that is utilized in a 600 MW IGCC power plant at Polk Power Station.
Others have proposed non-planar platen arrangements. In all of these designs, the platens are confined to an annular region of the furnace plan area within the RSC. The center of the furnace is open to allow large slag particles to fall through the RSC without excessive deposition on the platens.
To date, all RSCs in use suffer from one or more drawbacks including, but not limited to, less than optimal heat transfer, fouling issues, plugging issues, and/or size issues (i.e., are larger in size than desired in order to address and/or overcome various fouling and/or plugging issues).
Accordingly, there is a need in the art for a RSC device that is both more compact in nature and less apt to fouling and/or plugging issues.